Stars are made from a largecloud of
dust and gas called a nebula.
A nebula contains mainly
hydrogenwith smaller amounts of helium
and dust.

If the
mass of
hydrogen is large enough, the large amountof gravity will start to
pull the hydrogenin on
itself.
The cloud of gas will start to contract and
form a ball.
The ball of hydrogen is called a protostar.

As the
protostar continues to contract under its owngravity,
the hydrogen atomsaccelerate (see Newton's Second Law)
and their kinetic
energyincreases (they get faster).
The extra kineticenergyraises the
temperature of the hydrogen
and the atomscollide with each other more
frequently.

This
process continues until the hydrogen
atoms are movingso fast
that they
overcome the force of
repulsionbetween them
and undergo a nuclear reaction
called fusion
when they collide.Fusion turns hydrogen into helium
and releases a huge amount of energy
as heatandlight.
At this stage the protostarbursts into flame and a star is
born.